Standard manufacturing tolerances inherent in the threaded portions of conventionally threaded fasteners results in small air spaces between the mated male and female threads which allows the fastener combination to shift laterally or "rock" when subjected to vibration or shock. This lateral movement of the threads is sufficient to overcome starting friction between those portions of the thread which are in frictional contact with each other. When the fastener is tightened, a substantial amount of potential energy is stored in the threads (due to stresses), which is transformed into kinetic energy as the threads laterally shift with respect to each other thereby unlocking the threads and loosening the fastener. This undesirable situation is particularly acute in assemblies which are subjected to constant vibration, such as steering assemblies, drive trains, engines, etc.
Locking thread constructions have been devised in the past in an attempt to overcome the problem mentioned above. These past attempts have involved either filling the threads with vibration absorbing material or deflecting the threads in order to increase the level of friction therebetween. For example, one typical locking thread construction is shown in my prior U.S. Pat. No. 4,150,702 which discloses a fastener combination in which conventional male threads are deformed when mated with a special female thread. Although this previous fastener combination is suitable for many applications, it is less than completely desirable in other applications since not all the male threads mating with the female threads are deformed; the male threads remain permanently deformed, even after the female thread is removed, consequently, this type of fastener is not particularly desirable for use in those applications where the fastener must be disassembled to allow for repairs, adjustments, replacement, etc. of the fastened parts. Although the components of such a fastener may be replaced in those situations where disassembly is necessary, this unnecessarily increases both labor and material costs.
Accordingly, it is a primary object of the present invention to provide a locking thread construction which eliminates lateral or radial type movement of the threads relative to each other which can lead to loosening of the fastener and in which tight frictional engagement is achieved between the male and female threads for several revolutions of the circumference of the threads.
Another object of the invention is to provide a locking thread construction in which one of the threads is of conventional design and becomes at least partially deformed when the male and female components of the fastener are threadably mated.
A still further object of the invention is to provide a fastener of the type mentioned above in which the deformed thread is reformed to its original shape when the male and female components are unthreaded.
Another object of the invention is to provide a locking thread construction for a fastener as described above which is at least free-running to some extent in order to allow the male and female components to be initially hand-threaded, but yet which may be locked without drawing both the male and female components tightly against the parts being fastened.
These and further objects will be made clear or will become apparent during the course of the following description.